The spectre of Rome has returned. As far back as the Dark Ages, every Western culture sooner or later feels the need to reflect on its relationship with history's most celebrated civilisation, and now it's the turn of the MTV generation. Next month the BBC launches its grandiose 11-part series Rome - a co-production with American cable station HBO.

To justify its monstrous budget (£800,000 an episode for the BBC alone), publicists on both sides of the Atlantic have been talking up its unprecedented depictions of sex and violence, lavish sets and cutting-edge CGI. However, this history is rarely revelatory and the drama only a tad above the TV norm. What is more interesting is what this series tells us about modern America. For depictions of Rome time and again provide a historical canvas for the exploration of more contemporary concerns.

The saga opens in 52 BC. Gaius Julius Caesar is finishing off his conquest of Gaul, while back in Rome political machinations are at fever pitch in expectation of his return. The aristocracy, or 'Optimates', are fearful of Caesar's populism and form an alliance with the powerful Senator and military hero, Pompey Magnus. In the midst of all this, Caesar's niece, Attia, is trying to protect the family's dynastic interests with a potent blend of sexual cunning and marital alliances.

So far, so Gladiator: we have the contrast of military virtue with political back-stabbing on Palatine Hill. But what is original is the timescale. Both Ridley Scott's Gladiator and its 1964 precursor, The Fall of the Roman Empire, were set in the second century AD. It was in those decades - after the subduing of Germania - that the Roman Empire peaked and decline became inevitable. The tragedy of Marcus Aurelius (depicted by Alec Guinness in the 1964 version) was that he realised his incessant military adventures were undermining the true calling of Rome.

However, some 150 years previously, the republic is not concerned with such gloomy introspection. It stands on the cusp of greatness. And this cleverly allows Rome space to develop beyond the fa miliar story of decline and fall: with Brutus and Mark Anthony introduced as young men in the first programme, we know we're in for a satisfying epic.

The arrogance of Rome's military and political elite is reflected in a brazen amorality which the producers insinuate is the inevitable product of pagan worship. One sequence - which borrows heavily from the sacrifice scene towards the end of Apocalypse Now - erotically conjoins the slaughtering of a bull with intense sexual satisfaction. As such, the series is happily following a worthy cinematic tradition of offering up soft-porn under the guise of historical authenticity. No one did it better than Penthouse publisher Bob Guccione in his 1979 film, Caligula. With its liberal mixture of rape, fisting, and oral sex - along with a bizarre cameo by Peter O'Toole - it provided one of the more graphic renditions of Rome's final years.

In Rome, the violence is similarly graphic. Outside of the military arena, the republic is depicted as a place of easy and gratuitous brutality: knives are shoved in necks, characters butchered. However, the problem with the battlefield scenes is that since Gladiator audience expectations of combat sequences have risen far beyond what television budgets can provide. Meanwhile the programme's stream of violence undermines the dramatic flow. Indeed, it is the kind of easy thuggery which HBO's most famous creation, Tony Soprano, would enjoy. A man drawn to historical mini-series (mostly about Hitler), one can easily imagine Tony purporting himself as a latter-day Caesar.

It is that sense of effortless connection to the Roman world which has always drawn us back towards the republic. Two millennia on, we can still see ourselves reflected in the Romans. The Egyptians are too 'other'; the Greeks too worthy. But the Romans are human: tempestuous, sensuous, ambitious and political. For artists, they are a wonderful vehicle for the most outrageous fictions. Engagingly overblown characters set against luxurious backdrops, their lives provide ready-made fantasies of sexual debauchery and military bravado. As this series confirms, it is always with a frisson of excitement that Western culture turns to the Rome of gladiators, decadence, and forbidden delights.

But the story of Rome is more than a literary trope. The mesmerising history of its rise from city-state to global empire followed by excruciating decline culminating in the sack of Rome (455 AD) has served as a perpetual warning from the past. To medieval and Renaissance historians it was a morality tale of hubris and nemesis, testifying to the unrelenting cycle of history. What rose had to fall and no amount of statecraft could ever overcome the dictates of time.

It was the ambition of the Enlightenment historian Edward Gibbon to provide a more scientific answer. In 1764 he travelled to Rome and, 'as I sat musing amidst the ruins of the Capitol, while the barefooted fryars were singing Vespers in the temple of Jupiter, the idea of writing the decline and fall of the City first started to my mind.' What resulted was an epic six-volume account of Rome's collapse which set the standard for every subsequent history.

What has always attracted scholars and statesmen to Roman history is the search for the seeds of that decline. Was it military overstretch? Was it the cost of Empire? And, crucially, when did decline begin? In the early 1900s, British imperial politicians were mesmerised by the narrative of Rome in the hope of avoiding the same fate. Stationed as a cavalry officer in Bangalore, the young Winston Churchill spent lazy Raj afternoons 'devouring Gibbon' for the answers. Desperate for Britain to stave off decline, Churchill was adamant that a liberal Empire committed to peace, trade and civilisation could avoid the inevitable collapse.

And now America is having the same conversation. For the HBO series is simply television catching up with acres of commentary on whether America is indeed the new Rome. Pundits such as Charles Krauthammer and Niall Ferguson have long called upon America to accept its imperial status and the responsibilities which come with it. With its global dominions, militarist culture, and geo-political ambitions, America is an empire and should display some modest intelligence in looking to the past for answers to this complex role.

Certainly this is not the first time this debate has been popularly aired. In 1977 the peerless Robert Graves work I, Claudius was screened on PBS. Many took this account of a crumbling, internecine, back-biting Rome as an astute commentary on the Richard Nixon White House.

But the virtue of Rome is that it moves the action from Palatine Hill to the streetscape and in the process demystifies the nature of empire. Empire is not a state of being which a nation suddenly falls into: it is a slow process during which everyday life continues. So, we have the rather good depictions of Roman life: its insanitary realities, its bawdy popular culture, its social gradations.

Against the backdrop of what hurricane Katrina exposed about the modern American underbelly, this is the strength of the series: it shows how a global empire can co-exist with (and is arguably dependent upon) intense domestic inequality. As series producer Bruce Heller puts it: 'It [Rome] was a merciless existence, dog-eat-dog, with a very small elite, and masses of poverty.' As true of New Orleans and Washington today as Rome then.

So far, I have only seen the first episode of Rome and for me the real intellectual mettle of the series has yet to be tested. For Gibbon was clear: one of the defining causes of Rome's decline was the arrival of Christianity. This sapped the Romans of their martial spirit as the next world took precedence over this one.

Given the strength of evangelical Christianity within American popular culture, this will prove a contentious message for HBO to deliver. But, as ever with the story of Rome, it will reveal far more about current preoccupations than the real history of the Roman republic, its empire, or its people.

· Rome starts on BBC2, 9pm, 9 November. Tristram Hunt is a lecturer in history at Queen Mary College, London